Endocrine Abstracts

Antithyroid drugs (ATD) therapy is a common first-line treatment for Graves’ disease (GD). Patients are routinely counseled about rare side effects including agranulocytosis and pancreatitis. We report a rare case of myositis in association with ATD treatment in a patient with GD. A 37-year-old male with an acute presentation of symptomatic GD was commenced on carbimazole 30 mg daily in late November (TSH receptor antibody 9.2 Int Unit/l). He re-presented in January with progressively worsening muscle cramps, pain, and generalized weakness. Investigations showed deranged liver function tests, severely elevated creatinine kinase (CK) 15,920 Int Unit/l, and TFTs with a low FT4 at 6.0 pmol/l, TSH <0.01munit/ L, FT3, 4.3 pmol/l. Renal function and urinalysis were within normal limits. There were no clinical features of other systemic illness or inflammatory myopathy, and no obvious contributing medication including statins. The patient was treated with intravenous (IV) fluids, and carbimazole was discontinued. CK levels normalized after treatment with IV fluid and cessation of carbimazole. Following a period of observation, the free T3 rose, so a trial of low-dose Propylthiouracil was started to try and prevent full recurrence of the thyrotoxicosis. This was also associated with recurrence in muscle cramps and a moderate CK (2239) rise, so it was stopped. This patient underwent definitive treatment with a total thyroidectomy. There are a few case reports of carbimazole-associated myositis in the literature, but these document no similar symptoms when switching to alternative ATDs. Our case illustrates that caution is needed on trialing alternative ATDs in case of recurrence of myositis. We also reiterate the importance of considering an alternate diagnosis including inflammatory myositis, thyrotoxic myopathy, and thyrotoxic periodic paralysis. Finally, we highlight myositis and rhabdomyolysis as a rare complication of ATD therapy to increase clinician awareness and for early consideration of alternative definitive treatment in GD.